1. Field of the Invention
This invention relates, in general, to electronic color printers and, more specifically, to apparatus and methods for storing page data in memory buffers of electronic color printing devices.
2. Description of the Prior Art
The amount of memory needed to store information or data which is to be printed by a gray-scale, color printer can be extremely large when high quality printing is desired. The format in which the printers require the data is also involved in establishing the memory requirements for the printer. Ordinarily, the data for such printers is defined for a complete page before the data is processed and applied to the printhead or other device which creates the page image on a hard copy medium, such as a sheet of paper. Because of the wide range of colors which may be specified by the data, conventional memory arrangements and traditional bit-maps would have to be extremely large to accommodate data for high quality images.
Some data storage techniques use a limited number of colors to specify the color values used in defining the page. In such systems, a fixed number of colors are stored in a lookup table and the address of the color is stored in a page memory. When printing takes place, the processor goes to the indicated address in the lookup table and retrieves a multibit color value. The number of different colors which can be used with such systems is usually in the range of 256 to 512 total colors. While this type of storage may be sufficient in certain applications, some specialized applications may require color specification to a more precise degree in order to faithfully reproduce the image.
The maximum number of different colors which can be specified is dependent upon the number of bits used to define the color values. Twenty-four bits are used by some widely used color standards to specify colors. Such a bit level means that over 16,000,000 different color values can be specified. A lookup table containing all of these values would present an uneconomical requirement for memory space for most printers.
Although the number of different colors which can be defined is very large, one page may not have near that many colors existing on the page. Even a high quality page can be printed with fewer color choices, such as approximately 65,000 different colors. Such a number of color values is still large but can be accommodated by using special memory utilization techniques. A large number of colors required for quality representation is especially important with mixed mode page data wherein high resolution text/graphics lines exist on a background of shaded colors.
Therefore, it is desirable, and it is an object of this invention, to provide a data storage system for color printers which can preserve the resolution and quality of color content in the defined page without requiring an uneconomical amount of memory space.